This invention relates generally to the field of lead-acid batteries, and, more particularly, to an apparatus and a method for rapidly carrying out highly discriminating diagnostic tests on lead-acid batteries and charging such batteries if appropriate.
Over the years, the purchasing habits of customers for starting, lighting and ignition (xe2x80x9cSLIxe2x80x9d) batteries for automotive and other applications has changed. In the replacement market for SLI batteries, it has been increasingly the case that customers purchase such batteries at mass merchandisers and that warranties, often relatively expensive, are provided.
Accordingly, when a customer has problems starting his vehicle and suspects that the battery has gone bad, the customer returns the battery to the retailer or other location where the battery was purchased, and the warranty provided with the sale comes into play. A typical resolution is that the retailer takes the xe2x80x9cbad batteryxe2x80x9d back, providing a new battery.
Indeed, it seems that the battery gets the blame as the cause for the problem regardless. Yet, it has been found that a significant proportion of batteries perceived as bad, and thus replaced per the warranty, are in fact lacking in charge, but capable of being recharged so as to provide satisfactory performance in use. The warranty cost to both the retailer or other battery seller and to the battery manufacturer is substantial.
For this reason, mass merchandisers and other battery sellers have turned to various types of testing devices in an attempt to effectively distinguish between good and bad batteries. Some battery testers which have been used carry out simple fixed discharges to determine battery power. Such testers are a variation of a standard load test in the industry which discharges the battery at half its cold cranking rate for 15 seconds and then looks for a minimum voltage adjusted for temperature to determine whether the battery being tested is good or not. While such a standard test is relatively simple and straightforward, this test requires that the battery be highly charged, a condition usually lacking in batteries that are giving problems for whatever reason and are thus perceived as being bad. Such a standard test also requires a large sustained discharge current which, of course, discharges the battery significantly. Many commercial diagnostic testing units include a fixed resistor which discharges all batteries at a close-to-constant rate that is well below the load test. Acceptable voltages are either fixed or relative to the cranking rate of the battery.
Testing units can also combine charging with the discharge test. Charging usually is done with a straight fixed voltage or current charger from a simple transformer with a rectifying diode which tries to force charge into the battery no matter what its condition. Yet, charging a battery can mask defects such as shorted cells and the like. Further, when batteries with shorted cells or bad internal connections are charged substantially, there can be a great deal of gassing and spewing of electrolyte which can be dangerous.
Another type of test unit proposed and used is a unit providing a conductance meter. Using relatively small current probes, the internal conductance of the battery is measured. This internal conductance is assumed to be proportional to the cranking rate of the battery, therefore providing a relative performance criteria. However, this type of test unit does not stress or polarize the battery enough to determine if there is sufficient power to sustain a discharge for more than a brief instant and cannot accurately predict the full-charge performance when the battery being tested is in a heavily discharged condition. Such an analysis also provides no information about the chargeability of the battery being tested.
Accordingly, despite the clear need for a highly discriminating lead-acid battery diagnostic test unit, it is believed that none of the types of test units being used satisfy the need. The warranty problem is a major issue in the lead-acid battery field which has simply not been solved.
Indeed, the situation is perhaps exacerbated by the increasing role mass merchandisers play in selling SLI and other lead-acid batteries. More particularly, the personnel responsible for dealing with battery returns not only do not have discriminating test units at their disposal, but are often less than adequately trained to deal with the many issues underlying whether a battery being returned is bad or good.
Still further, in many situations, the lack of patience of the customer can be evident. A decision as to whether the battery is good or bad needs to be capable of being provided in a relatively short period of time. Additionally, if the battery is determined to be good but in a discharged condition, then the customer will want to have the battery recharged in as short a time as possible.
Given the many and varied parameters that need to be addressed to allow a highly discriminating diagnostic testing regiment to take place and to rapidly recharge acceptable batteries, providing a suitable diagnostic test unit which can be safely used by the responsible personnel is a formidable task. Accordingly, it is a primary object of the present invention to provide a method and apparatus capable of rapidly discriminating between good and bad lead-acid batteries. A more specific object of this invention provides a test regiment capable of carrying out the appropriate determination in no more than 15, and still more preferably less than 10, minutes.
Another object lies in the provision of a diagnostic test unit capable of testing various types of lead-acid batteries having a variety of capacities as well as conditions while appropriately discriminating between good and bad batteries.
Still another object of the present invention provides a diagnostic test unit which can be operated by personnel with limited training at most.
Yet another object of the present invention provides a diagnostic test unit characterized by safety features which minimize, if not eliminate, safety issues as regards both users and as to the test units themselves.
A more specific object of this invention lies in the provision of a diagnostic test unit which includes an interactive charging unit capable of rapidly and reliably recharging lead-acid batteries.
Other objects and advantages will become apparent from the following detailed description.
In general, the present invention provides a straightforward diagnostic test unit and system which automatically and rapidly takes advantage of the known phenomenon that battery resistance can be characterized by discharging at various rates and measuring the resulting voltage. Thus, as is known, the current versus voltage relationship is linear and the proportionality constant is the resistance (or inversely the conductance) of the battery in a discharging mode. This can also provide a derived voltage at vanishing current which represents the polarized potential of the battery. According to the present invention, the diagnostic test unit utilizes a charger combined with a rapidly variable load. Each is controlled by signals to and from a microprocessor; and, additionally, an input display provides directions to, and derives information from, the system operator. After inputting the battery type (12V or 6V), the cold cranking rating (xe2x80x9cCCAxe2x80x9d) or cranking rating (xe2x80x9cCAxe2x80x9d), and providing the temperature of the battery, a diagnostic ramp procedure is utilized to provide an instantaneous current versus voltage analysis to determine the instantaneous CCA (i.e., the single crank capability at full charge) of the battery being tested. If the instantaneous CCA of the battery being tested is above a level determined acceptable, a sustained discharge is carried out to tax the capacity of the battery.
The amount of time held at this sustained discharge rate is proportional to the determined instantaneous CCA of the battery and the temperature. Small batteries with low CCA rates are discharged a shorter time than large CCA batteries while cold batteries are discharged for a shorter period of time than are hot batteries.
At the end of the constant current discharge, the current is again ramped from a high level to a lower level to determine a loaded or polarized CCA which simulates the battery power after multiple cranking attempts. If the loaded CCA (i.e., the single crank capability at the present state of charge of the battery) is below a desired percentage of the rated capacity, then the battery is put into charge. It has been found that a battery does not have to be charged very much to respond acceptably to these ramping probes. Indeed, if a battery cannot be acceptably charged within the time of a given number of diagnostic probes, the battery is deemed to be a bad battery.
In accordance with the preferred embodiment of the present invention, the charging steps utilized during the diagnostic testing, as well as any charging of batteries determined to be good, utilizes a novel interactive stepping procedure which allows batteries determined to be good to be recharged in a minimum period of time without overheating the battery or spewing electrolyte.
Additional features and advantages of the invention will be made apparent from the following detailed description of illustrative embodiments which proceeds with reference to the accompanying figures.